ABSTRACT

The increasingly worldwide problem regarding rapid economy development and a relative shortage of energy, recently the internal combustion engine exhaust waste heat and environmental pollution has been more emphasized heavily. In an internal combustion engines; efficiency of engine is around 30 %, roughly 30% of the fuel energy is wasted in exhaust gases, and 30% in cooling water and 10%are unaccountable losses. Efforts are made to catch this 30% energy of exhaust gases. Waste heat release in the form of fumes in environment through I.C engine. The side effects are global warming, greenhouse effects and entropy increases etc. Therefore, it is required to use the waste heat in to useful work. The recovery of waste heat not only conserves fossil fuel but also control the environment pollution. Therefore, main objective of this project is to demonstrate (waste heat recovery system) technology based on the total waste heat converted into the useful mechanical work and possible methods to recovery of the waste heat from I.C engine. If this waste heat energy is tapped and converted into usable energy, the overall efficiency of an engine can be improved. Thermoelectric modules which are solid state devices that are used to convert thermal energy to electrical energy from a temperature gradient and it work on principle of Seebeck effect. As a result, waste heat recovery from the I.C engines and utilization shall be remain best technique in future automobile application save the fuel and protect the environment.

INTRODUCTION

The I.C engine is a device which converts the chemical energy of fuel into heat and again heat energy in to mechanical work. It is the fact that the total heat supplied to the engine in the form of fuel approximately only 30-40% get converted in to useful mechanical work and remaining almost 70% of the energy released from fuel due to combustion is lost mainly in the form of Heat. Approximately 25-30% of the total energy generated by the engine is dissipated in the form of Exhaust loss energy. Increase in economy the energy demand also increases which results in more usages of fossil fuels which causes the emission of harmful greenhouse gases. Large amount of heat is released in the atmosphere from the engines without utilizing for any purpose. If some amount of this waste heat could be recovered it possible to reduce the primary fuel required. Waste heat utilization is the major source of cost saving. If exhaust gases of engines are directly released into atmosphere it will not only waste heat but also causes the environmental problems, so it is required to utilize the waste heat for useful work to increase the efficiency of engine.The- recovery and utilization of waste heat from engine results in reduction in fuel consumption, reduction in waste heat loss and engine emission, increases the engine efficiency. It is necessary that continuous and serious efforts should be taken for conserving this waste heat by using proper waste heat recovery techniques. This project shows, Heat available from engine exhaust and existing and possible waste heat recovery systems for I.C engine .Benefits of waste heat recovery from engines can be broadly classified in two categories

Direct Benefits:

Recovery of waste heat has a direct effect on the combustion process efficiency. This is reflected by reduction in the utility consumption and process cost.

        Indirect Benefits:

1) Reduction in pollution: A number of toxic combustible wastes such as carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NOx), and particulate matter (PM) etc, releasing to atmosphere. Recovering of heat reduces the environmental pollution levels.

2) Reduction in equipment sizes: Waste heat recovery reduces the fuel consumption, which leads to reduction in the flue gas produced. This results in reduction in equipment sizes.

3) Reduction in auxiliary energy consumption: Reduction in equipment sizes gives additional benefits in the form of reduction in auxiliary energy consumption

                                                

                                                                                          

LITERATURE REVIEW

According to the experimental analysis conducted by Suryawanshi et al., the temperature of pipe surface of exhaust gases flowing through exhaust gas pipe is very high and it is around 2000C to 3000C so a heat exchanger is made, which conducts heat from exhaust pipe to thermoelectric modules, one surface of these modules is in contact with the surface of hot side heat exchanger and other is in contact with the surface of cold side heat exchanger and thus potential difference is created and power is produced due to Seebeck effect.

Yu and Chau.,has proposed and implemented an automotive thermo-electric waste heat recovery system by adopting a Cuk converter and a maximum power point tracker (MPPT) controller into its proposed system as tools for power conditioning and transfer. They reported that the power improvement is recorded from 7.5% to 9.4% when the hot-side temperature of the TEG is heated from1000C to 2500C. Also, when the hot-side temperature of the TEG is fixed at 2500C, the power improvement as much as 4.8% to 17.9% can be achieved.

Baskar et al.,did an experiment to study and analyze the feasibility of retrofitting the waste heat recovery system to a two stroke petrol engine. The experimental performance testing has shown that the overall efficiency of two stroke petrol engine installed with and without the waste heat recovery system is 29.67% and 29.2% respectively when the power extraction was 90W. The combined heat and power system offers additional benefits like reduction in the emission of carbon dioxide (CO2), sulphur dioxide (SO2) and oxides of nitrogen (NOx) for the same power and heat generation

Jadhao et al., in his paper had analyzed the possibility of heat recovery from an IC engine and the various ways to achieve it. He has compared the various possibilities like the Thermo electric generation, Thermo Ionic Generation and Piezoelectric Generation. He found that in Thermo Electric generation, optimal temperature difference is sufficient to produce the required power. It would also help to recognize the improvement in performance and emissions of the engine. If these technologies were adopted by the automotive manufacturers then it will be result in efficient engine performance and Low emission.

PrathameshRamade et al.,  Automobile Exhaust Thermo-Electric Generator Design, Experimental work was carried out to study the performance of thermoelectric generators under various engine speeds. At high vehicle speeds, the total power extracted was more. More power could also be extracted by improving the exhaust gas heat exchanger. At high vehicle speeds, the total power that could be extracted was increased. More power could also be extracted by improving the exhaust gas heat exchanger. At the engine speed of 3970 RPM, the power generated was 15.12W and efficiency of the system was 5.0708%.

ADVANCED METHODS OF WASTE HEAT RECOVERY

Increasing of fuel costs and diminishing petroleum supplies are focusing governments and industries to increase the power efficiency of engines. There are several technologies for recovery this energy from C.I engine, where as a controlling ones are: Waste heat can be used for power generation purpose, refrigeration purpose and heating purpose etc.Waste heat of exhaust gas of engine can be used for generating mechanical work output. This can be developed directly by thermoelectric generator .

              The AETEG works on the principle of thermoelectricity: when the junctions formed by joining two dissimilar current carrying conductors are maintained at different temperatures, an electro motive force (emf) is generated in the circuit. The current carrying conductors are known as thermoelectric elements and the couple formed out of the two current carrying conductors is known as thermoelectric couple. In a typical generator heat exchangers are used to transfer heat from the heat source and the sink to junctions of the thermocouple. The heat exchangers and the thermoelectric couple unit is known as a thermoelectric generator (TEG). The AETEG has the vehicle exhaust gas as its heat source and the engine coolant as its heat sink. Thermoelectric conversion is a solid-state technology with no moving parts, which is simple and reliable.

METHODOLOGY

                    Fig;  block diagram

                                    

           The vehicle is started and the acceleration is to be given, so that the amount of heat leaving the exhaust will be increased. Due to this heat, the surface of the exhaust pipe and the silencer will be heated to very high temperatures. These hot surfaces will try to liberate the heat to the atmosphere, which acts as a Heat Sink. Since the atmospheric temperature is less than that of the silencer surface, a temperature difference is created and hence the surface tries to attain the equilibrium state through the heat transformation process. But this will take much longer time.

Hence in order to increase the rate of heat transfer the Thermal Grease is used. The Thermal Grease is coated on the hot surface of the silencers and also in the inner surface of the fins which are present in the upper part. The fins are also used to increase the heat transfer rate. As the vehicle moves, the air flow will take place between the fins and it acts as the sink

As the surface of the silencer gets more and more heated the heat transfer rate will increase due to the increase in the temperature difference. The Peltier module is placed between the Heat Source (Hot Silencer Surface) and the Heat Sink (atmosphere) and the fins are placed above the module. The module is made of semiconducting materials.

 Hence by the principle of Seebeck Effect, the temperature difference can be directly converted into voltage by using some thermoelectric materials. Based on this effect, when the surface heat of the silencer is passed on to the atmosphere, the electrons and holes of the thermo electric semiconductors will try to move towards the junction and make the flow of electric current to be possible.

The voltage developed due to this effect can be increased by using some Booster circuit like DC-DC Cuk Converter. This will step up the voltage generated to some nominal value. So that we can get the sufficient amount of voltage.

Hence this voltage can be connected to some battery and stored, or else it can be given directly to some electric appliances which uses DC. If we need AC voltage, it can be converted using the rectifier. The voltage generated can be increased by placing more number of modules and connecting them with one another to meet the demand of the required voltage. This voltage can then be supplied to the suitable electrical appliances

ADVANTAGES AND LIMITATIONS

Advantages

·         Thermoelectric to generate electricity for powering auto components such as lights, control system, GPS, electronic system and electronic braking etc.,

·         Improve fuel economy upto 5%. When engine runs in an automobile, battery is charged so that it can utilized for electrical appliances. But when TEG is used, it generates electricity and thus fuel efficiency can be increased.

·         Reduce Regulated Emissions and Greenhouse Gases.

                   

Limitations

·         Thermoelectric generator generate less electric power for the same heat flow i.e. they have low efficiency as compare to other mechanical power generator.

·         Thermoelectric generators are costly as compare to other generator.

·         Requires relatively constant heat source.

·        Low thermal characteristics. By heat dissipation any device depends upon on its thermal conductivity.

CONCLUSION

In this project we have successfully fabricated an exhaust gas heat recovery power generator. Thus the eco-friendly power generation method can be implemented for domestic and commercial use at an affordable cost.

The efficiency of the engine will not be affected because only the surface heat of the silencer is drawn out. The main objective of this paper is to recover the surface exhaust heat to avoid the accidents (Burn-outs) caused by the overheated silencers, and to convert the recovered heat to useful electric energy.

 This objective has been successfully accomplished in this project. The output could be increased by connecting a number of TEGs in series, so that the voltage gets added up leading to increased power. The energy produced from this system could be used to power any auxiliary devices in an automobile directly or it could be stored in a battery and then used later.